On fog formation in a coronal discharge: effects of the discharge on droplet growth

When water vapor in moist air reaches supersaturation in a transonic flow system, non-equilibrium condensation forms a large number of droplets which may adversely affect the operation of some thermal-hydraulic equipment. For a better understanding of this non-equilibrium condensing phenomenon, a numerical model is applied to analyze moist air condensation in a transonic flow system by using the theory of nucleation and droplet growth. The Benson model is adopted to correct the liquid-plane surface tension equation for realistic results. The results show that the distributions of pressure, temperature and Mach number in moist air are significantly different from those in dry air. The dry air model exaggerates the Mach number by 19% and reduces both the pressure and the temperature by 34% at the nozzle exit as compared with the moist air model. At a Laval nozzle, for example, the nucleation rate, droplet number and condensation rate increase significantly with increasing relative humidity. The results also reveal the fact that the number of condensate droplets increases rapidly when moist air reaches 60% relative humidity. These findings provide a fundamental approach to account for the effect of condensate droplet formation on moist gas in a transonic flow system.

Download Full-text

A Heat Transfer Model of Dropwise Condensation Underneath a Horizontal Substrate

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.199-200.1604 ◽

2011 ◽

Vol 199-200 ◽

pp. 1604-1608

Author(s):

Yun Fu Chen

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Contact Angle ◽

Fractal Model ◽

Condensation Heat Transfer ◽

Droplet Growth ◽

Transfer Model ◽

Dropwise Condensation ◽

Small Contact Angle ◽

Horizontal Substrate

For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.

Download Full-text

Crossover, locking-in, and intermittency of droplet growth rates in phase separation

Physical Review A ◽

10.1103/physreva.30.1052 ◽

1984 ◽

Vol 30 (2) ◽

pp. 1052-1059 ◽

Cited By ~ 20

Author(s):

Hiroshi Furukawa

Keyword(s):

Phase Separation ◽

Growth Rates ◽

Droplet Growth

Download Full-text

Mixing state and compositional effects on CCN activity and droplet growth kinetics of size-resolved CCN in an urban environment

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-10239-2012 ◽

2012 ◽

Vol 12 (21) ◽

pp. 10239-10255 ◽

Cited By ~ 40

Author(s):

L. T. Padró ◽

R. H. Moore ◽

X. Zhang ◽

N. Rastogi ◽

R. J. Weber ◽

...

Keyword(s):

Chemical Composition ◽

Water Soluble ◽

Anthropogenic Sources ◽

Droplet Growth ◽

Mixing State ◽

Aerosol Composition ◽

Activation Kinetics ◽

Aerosol Mixing State ◽

Kinetics Of ◽

Ccn Activity

Abstract. Aerosol composition and mixing state near anthropogenic sources can be highly variable and can challenge predictions of cloud condensation nuclei (CCN). The impacts of chemical composition on CCN activation kinetics is also an important, but largely unknown, aspect of cloud droplet formation. Towards this, we present in-situ size-resolved CCN measurements carried out during the 2008 summertime August Mini Intensive Gas and Aerosol Study (AMIGAS) campaign in Atlanta, GA. Aerosol chemical composition was measured by two particle-into-liquid samplers measuring water-soluble inorganic ions and total water-soluble organic carbon. Size-resolved CCN data were collected using the Scanning Mobility CCN Analysis (SMCA) method and were used to obtain characteristic aerosol hygroscopicity distributions, whose breadth reflects the aerosol compositional variability and mixing state. Knowledge of aerosol mixing state is important for accurate predictions of CCN concentrations and that the influence of an externally-mixed, CCN-active aerosol fraction varies with size from 31% for particle diameters less than 40 nm to 93% for accumulation mode aerosol during the day. Assuming size-dependent aerosol mixing state and size-invariant chemical composition decreases the average CCN concentration overprediction (for all but one mixing state and chemical composition scenario considered) from over 190–240% to less than 20%. CCN activity is parameterized using a single hygroscopicity parameter, κ, which averages to 0.16 ± 0.07 for 80 nm particles and exhibits considerable variability (from 0.03 to 0.48) throughout the study period. Particles in the 60–100 nm range exhibited similar hygroscopicity, with a κ range for 60 nm between 0.06–0.076 (mean of 0.18 ± 0.09). Smaller particles (40 nm) had on average greater κ, with a range of 0.20–0.92 (mean of 0.3 ± 0.12). Analysis of the droplet activation kinetics of the aerosol sampled suggests that most of the CCN activate as rapidly as calibration aerosol, suggesting that aerosol composition exhibits a minor (if any) impact on CCN activation kinetics.

Download Full-text

Droplet Growth and Transition to Coalescence in Confined Geometries

Langmuir ◽

10.1021/la0603267 ◽

2006 ◽

Vol 22 (13) ◽

pp. 5630-5635 ◽

Cited By ~ 4

Author(s):

Peter A. Kottke ◽

Audric Saillard ◽

Andrei G. Fedorov

Keyword(s):

Droplet Growth ◽

Confined Geometries

Download Full-text

The Feasibility of an Euler-Lagrange Approach for the Modelling of Wet Steam

Volume 2C: Turbomachinery ◽

10.1115/gt2020-16199 ◽

2020 ◽

Author(s):

Tim Wittmann ◽

Christoph Bode ◽

Jens Friedrichs

Keyword(s):

Optimal Parameter ◽

Nucleation Theory ◽

Classical Nucleation Theory ◽

Droplet Growth ◽

Wet Steam ◽

Discrete Phase Model ◽

Ansys Fluent ◽

Validation Data ◽

Numerical Validation ◽

Lagrange Approach

Abstract This study investigates the applicability of an Euler-Lagrange approach for the calculation of nucleation and condensation of steam flows. Supersonic nozzles are used as generic validation cases, as their high expansion rates replicate the flow conditions in real turbines. Experimental and numerical validation data for these nozzles are provided by the International Wet Steam Modelling Project of Starzmann et al. (2018). In contrast to most participants of that project, an Euler-Lagrange approach is utilized for this study. Therefore, the classical nucleation theory with corrections and different droplet growth laws is incorporated into the Discrete Phase Model of ANSYS Fluent. Suggestions for an efficient implementation are presented. The Euler-Lagrange results show a good agreement with the experimental and numerical validation data. The sensitivities of the Euler-Lagrange approach to modelling parameters are analysed. Finally, an optimal parameter set for the calculation of nucleation and condensation is proposed.

Download Full-text

mmBCFA C17iso ensures endoplasmic reticulum integrity for lipid droplet growth

The Journal of Cell Biology ◽

10.1083/jcb.202102122 ◽

2021 ◽

Vol 220 (11) ◽

Author(s):

Jingjing Zhang ◽

Ying Hu ◽

Yanli Wang ◽

Lin Fu ◽

Xiumei Xu ◽

...

Keyword(s):

Energy Homeostasis ◽

Membrane Integrity ◽

Lipid Synthesis ◽

Droplet Growth ◽

Side Chain ◽

C Elegans ◽

Branched Chain Fatty Acids ◽

Intracellular Organelles ◽

Branched Chain ◽

Er Homeostasis

In eukaryote cells, lipid droplets (LDs) are key intracellular organelles that dynamically regulate cellular energy homeostasis. LDs originate from the ER and continuously contact the ER during their growth. How the ER affects LD growth is largely unknown. Here, we show that RNAi knockdown of acs-1, encoding an acyl-CoA synthetase required for the biosynthesis of monomethyl branched-chain fatty acids C15iso and C17iso, remarkably prevented LD growth in Caenorhabditis elegans. Dietary C17iso, or complex lipids with C17iso including phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol, could fully restore the LD growth in the acs-1RNAi worms. Mechanistically, C17iso may incorporate into phospholipids to ensure the membrane integrity of the ER so as to maintain the function of ER-resident enzymes such as SCD/stearoyl-CoA desaturase and DGAT2/diacylglycerol acyltransferase for appropriate lipid synthesis and LD growth. Collectively, our work uncovers a unique fatty acid, C17iso, as the side chain of phospholipids for determining the ER homeostasis for LD growth in an intact organism, C. elegans.

Download Full-text